dan cayan, scripps institute for oceanogrphy & usgs
TRANSCRIPT
key points
•Drought and Flood are a common occurrence in California, 2012-2015 Drought is intense and warm as well as dry
•The absence of very large storms drives California dry (and wet) spells
• Climate change will likely exacerbate stresses on water resources
Climate Change Will Stress California’s Already Volatile Water Supply
Dan Cayan with Mike Dettinger, Mary Tyree, Sam IacobellisScripps Institution of Oceanography and USGS
UC Davis Oct 2015
Sierra discharge highly variable stddev/mean = 0.44 lowest 1977 highest 1983
But ,Columbia dischargeis quite steady, stddev/mean = 0.19
Annual discharge varies considerably in the Sierra Nevada
and Colorado dischargeis intermediately variable, stddev/mean = 0.33
Cayan et al 2003
California and much of western region has been more-or-less dry since 1999 observed precipitation departure (% of average), 1998-99 thru 2013-14
% departure from1981-2010 average
U.S. Drought Monitor/National Weather Service Hanford
Dettinger and Cayan Drought and the Delta—A Matter of Extremes accepted, San Francisco Estuary and Watershed Science, April 2014
a few large storms (or their absence) account for a disproportionate amount of California’s precipitation variability
5yr smoother
LARGE STORM CONTRIBUTION
95%ile
Recent dry years have mostly been warmer than normal. 2013-14 was exceptionally warm.
Precipitation Departure during dry years
Temperature Departure during dry years
2013-14
Anomalous warmth during winter 2014-15
virtually all climate simulations project warming, but with a wide envelope of temperature change
+3°C
CMIP5 GCMs project +3°C summer warming by 2060, under mid and high RCPs
14 GCMs X 3 RCP Emissions Scenarios IPCC 5th Assessment (CMIP5) models
July Temperature change Sacramento
Need to kmow
Which emissions pathway will we take?
How much summer amplification of warming?
How will temperature change inNear term?
Sierra Snowpack has been extremely low 2015 and 2014 spring snowpack disproportionately light
Dettinger and Anderson SFEWS 2015
Loss of California Spring Snowpack from 21st Century warming
•Under this scenario, California loses half of its spring (April 1) snow pack due to climate warming. Less snow, more rain, particularly at lower elevations. The result is earlier run-off, more floods, Less stored water. This simulation by Noah Knowles is guided by temperature changes from PCM’s Business-as-usual coupled climate simulation. (this is a low-middle of the road emissions and warming scenario)
Knowles, N., and D.R. Cayan, 2002: Potential effects of global warming on the Sacramento/San Joaquin watershed and the San Francisco estuary. Geophysical Research Letters, 29(18), 1891.
Declining odds of median or higher snowpack
Source: Cayan et al. (2011)
Drier Summer Landscapesincreased warming and diminished snowcauses successively greater soil drying
throughout 21st Century
(this picture could change somewhat under more recent CMIP5 simulations)
early 21st
middle 21st
late 21st
Cayan et al. Ch 6 Southwest Climate Assessment
Projected patterns of precipitation changes2090-2099 versus 1980-1999
Globally, dry regions become drier?
Although the number of wet days is projected
to decrease with climate change,
the intensity of the largest wet days is projected to increase !
Suraj Polade Polade, S.D., Pierce, D.W., Cayan, D.R., Gershunov, A., and Dettinger, M.D., 2014, The key role of dry days in changing regional climate and precipitation regimes: Nature Scientific Reports, 4:4364, 8 p., doi:10.1038/srep04364.
28 CMIP5 RCP 8.5 GCMs (2060–2089) vs. (1960-1989)
• California’s climate is prone to year-to-year and longer term variation in precipitation—drought is an expected part of our climate..
• California’s current dry spell has built up over multiple years, a more/less dry pattern has been in place since 1999.
• The absence of a few very large storms is often a key driver of dry years. And large storms are frequently involved in “busting” drought.
.
• Continued, substantial climate warming is highly likely but changes in annual precipitation is not well understood in California. However, climate change may shift precipitation characteristics—fewer overall wet days but more intense heavy events.
• In addition to the present ongoing dry spell, recurrent wet and dry events and episodes, in the midst of warm temperatures will provide future learning opportunities.
Summary
Whole CONUS PDSI
CA/NV PDSI
California/Nevada droughtonly moderately correlated w whole U.S.
PDSI from NCDC divisional dataset
ground waterwithdrawl increases
greatly in dry years
Dry Year
Typical Year
Faunt et al 2009 USGS
pumping
How are droughts made?
>80%
Mike Dettinger
California’s large yearly variation in precipitation is dictated by the presence or absence of storms during a
narrow seasonal window
California has only about 120 days to accumulate two thirds of its annual precipitation. When Pacific winter stormsAre diverted from California (as last winter) dry conditions result.
California year-to-year variation in precipitation is has the most volatile!of the entire U.S.
Cayan et al.2003
Multi-year dry spells are quite common in California Sacramento Drainage Divi standardized precip index 1900-2014 showing Intensity and Duration
Anne Steinemann et al. 2015 J. HydroMet. in press
Calif dought footprint is quite broad in western U.S. Sierra flows often in same phase (wet or dry)
as the Columbia or the Colorado
Low Sierra flows associated with large regional pattern
Cayan et al.2003
Sierra Nevada Annual PrecipitationCoef of Variation ~31.5%
mean 39.1 inches std dev 12.3 inches
2012-2014 dry spell is characteristic of California’s volatile precipitation climate
WY 2014 precip estimated at 65% of LT mean
From California Climate TrackerWestern Regional Climate Center
California has a narrowseasonal window to generate its annual water supply.
If atmospheric conditions areunfavorable during that period, a dry year results
prevalence of anomalously warm daytime temperatures
during cool season monthsof drought years
Sacramento Drainage DivisionDark bars are from 20% driest years
Pale bars are all years 1895-2014
CA1
ACCESS 1.0
CMCC CM
CMCC CMS
Climate Models indicate occasional
drought for CaliforniaIn 21st Century
Recent Water Loss over Western U.S. Surface displacements from GPS network show progressive uplift due to water mass loss in drought
GPS estimate by Borsa et al showing deficit of ~240km**3 water in March 2014 relative to 2003-2014 baseline over western U.S., west of 109°W. This is in general agreement with GRACE satellite observations, S. Castle et al 2014 GRL found ~65km**3 water water loss in Colorado Basin during 2004-2013.
Borsa et al. 2014
Meko, D.M., Woodhouse, C.A., and Touchan, R., 2014, Klamath/San Joaquin/Sacramento hydroclimatic reconstructions from tree rings: Report to California DWR 4600008850, 117 p.
1100 years of Sacramento River Discharge little overall change but considerable variability and multi-year spells reconstructed from tree ring records bu Dave Meko and colleagues, Univ Arizona
prevalence of anomalously warm daytime temperatures
during cool season monthsof drought years
Sacramento Drainage DivisionDark bars are from 20% driest years
Pale bars are all years 1895-2014
Co- occurrences of high (h) and low (l) annual Columbia, Sierra, Colorado discharge anomaly magnitudes > 0.7 1906-1999; anomalies +0.7 standard deviations above long-term means are counted as high, more than –0.7
standard deviations below normal are counted as low.
Sierra
h l
Columbia
h 8 3
l 2 13
How often do extreme annual flows co-occur in Sierra, Columbia, Colorado?
Sierra
h l
Coloradoh 13 4
l 2 16
Sierra and Columbia High and especially low flows co-occur. Relatively few Years when they have Opposing anomalies
Sierra and Colorado High and especially low flows co-occur. Relatively few Years when they have Opposing anomalies
Cayan et al.2003
34
Atmospheric Rivers West Coast flood generators
SummaryDrought Characteristics •California’s climate is prone to year-to-year and longer term variation in precipitation—drought is expected..
•California’s current dry spell has built up over multiple years, a more/less dry pattern has been in place since 1999.•Temperature during cool seasons of drought years—in recent decades, has more often been warmer than cooler than average. As with precipitation,, anomalous temperature strongly controlled by atmospheric circulation
Drought prediction is a challenge:•The absence of a few very large storms is often a key driver of dry years. And large storms are frequently involved in “busting” drought.
•there is not a unique atmospheric drought-circulation pattern..
•Anomalous Pacific SST patterns, tropical and extratropical appear in advance, during and after strong drought circulation months, but signals are somewhat weak.
500mb height anomalies averaged, all months during Dry years
ENSO vs. California PrecipitationSouthern California
K. Redmond et alWestern Regional Climate Center
K. Redmond et alWestern Regional Climate Center
Nino 3.4 hatched regionNino 3.4 SST
Number dry yrs Drought years occur duringAll phases of ENSO
PDO SST Anomaly Pattern
K. Redmond et alWestern Regional Climate Center
Number dry yrs
PDO Index
Drought years occur duringboth phases of PDO
over 21st Century occurs a marked decline of chances of reaching or exceeding historical median
Snow Water Equivalent Sierra Nevada+
10%
….and, chances of historical 10th percentile or less SWE increases greatly
40%
Median Apr 1 SWE 11.9cm
10th % Apr 1 SWE 3.6cm